In a slurry polymerization process, it is common to separate polymer from diluent in a pressure vessel by flashing off the diluent overhead and recovering the polymer via gravity. Most of the separation vessels operate fairly well when there is a sufficient pressure differential available across such vessels. See U.S. Ser. No. 11/724,890, filed Mar. 16, 2007 “Method and Apparatus for Separation of a Polymer Slurry.” However, when the available pressure differential is reduced such as in the case of using multi-stage separation to reduce energy consumption, polymer can potentially accumulate in the vessel and eventually plug and foul equipment, causing operability problems that interrupt the operation of the reactor.
The polymer that accumulates can be so called “amorphous” polymer, or simply polymer that has formed agglomerates such that large chunks of the polymer can no longer cycle through the reactor system and plugs one or more operating lines or openings. Also, polymer may adhere to the inside surface of the reactor system and accumulate to such a degree that the system is fouled. It is known in the art that such fouling can be inhibited within the reactor using certain catalyst inhibitors or “killers”. For instance, it is disclosed in WO95/07941 that various low molecular weight compounds such as amines, ethers, carbon dioxide, and others can be used to deactivate catalyst at the downstream side of the reactor or before a separation and compression stage in a high pressure polymerization process. See also WO93/25590 and WO04/026923. It is particularly well known to use catalyst killers such as amines and other compounds in gas phase reactor systems, such as disclosed in U.S. Pat. No. 6,111,034, U.S. Pat. No. 6,335,402, EP 0 811 638 A2, EP 0 927 724 A1, and WO03/042253. A method for the inhibition of the formation of polymer agglomerates or “popcorn” is found in U.S. Pat. No. 5,420,239.
What is needed is an improved method of inhibiting polymer agglomeration and fouling within the separation section downstream of a polymerization reactor that improves the overall service factor of a production train. There is a particular need for such a method in slurry-type polyolefin reactors which operate at relatively low pressures compared to high pressure processes and the polymer in suspension can easily agglomerate as unreacted monomers are removed.